The invention relates to an adjustable
throttle valve, comprising a one-piece or multi-piece housing, and having a control part and a throttle part, the throttle part containing a valve comprising an axially movable, hydraulically actuated follow-up throttle piston which, on the one side, links a supply channel via an annular restrictor to a service channel, the annular restrictor being formed between a bearing surface of the follow-up throttle piston and a corresponding seat of the housing and being open to a greater or lesser extent according to the axial position of the follow-up throttle piston, and which, on the opposite side, exhibits a hydraulically pressurised pressure shoulder which is linked, by an inlet channel with restrictor, to the supply channel and, by an outlet channel, to the service channel, the outlet channel exhibiting an aperture, which can be regulated via the control part, for regulating the pressure acting upon the pressure shoulder, which pressure determines the movement and position of the follow-up throttle piston.
Adjustable proportional throttle valves with feedback are commonly known and find application in all hydraulic assemblies. Amongst the many applications, there are various, e.g. hydraulic presses and large cranes, with which, despite the size of the plant and the magnitude of the hydraulic operating pressure, very precise movements have to be carried out and accordingly high demands are placed upon the precision and accuracy of the mode of operation of the throttle valves.
The known throttle valves according to a prior art, however only accomplished these requirements partially or inadequately. Firstly, these throttle valves required excessive regulating forces in the control part, which is disadvantageous from the economic viewpoint. Secondly, the known throttle valves possessed over-long switching times for the various applications, which put their use into question. Moreover, these known throttle valves were subjected to high wear and tear, so that their working life was too short.
In Document LU-84377 corresponding to U.S. Pat. No. 4,662,600, a descriptron is thus given of an adjustable proportional throttle valve, with which the costly pilot control system with power feedback is slim intend and the structural size can be reduced, whilst still maintaining the advantages offered in principle by these valves.
The principal concept of the invention described in that document consisted in making use of the oil pressure of the actual work system as a servo-energy supplier for the actuation of those valve components which, through the throttle valve, determine the volume flow, thereby, in addition to other benefits, substantially relieving the control part. This was able to be realised by virtue of a follow-up throttle piston arrangement.
For the characteristics of the mode of operation of the valve presented in the cited document, reference is made to this document.
The object of the present invention is to improve this last-mentioned valve by quite substantially reducing the valve-switching times and decisively improving the repetitive accuracy.